This invention relates to an image display apparatus, and more specifically to, an image display apparatus using a display panel such that a display area is formed between a pair of substrates, and process for its production.
The so-called panel-type image display apparatus with characteristics of being a thin shape, lightweight, and/or low consumption power is widely adopted for a personal computer, mobile information equipment, such as a cellular phone, or a monitor of a television receiver. For this kind of image display apparatus, one using a liquid crystal display panel, one using an organic electroluminescent panel (hereinafter referred to as the “organic EL panel”), one using a plasma display panel, and one using a field emission display panel, etc. are known.
The panel-type image display apparatus comprises normally the display area in which a large number of pixels each composed of a semiconductor layer constituting an active element and a fluorescent layer or an emitting layer are arranged in a matrix form between a pair of substrates at least one of which has light transmissivity, such as a glass, and is constructed by sealing a surrounding area outside this display area (hereinafter referred to as the “outer area” for simplicity) to be airtight using a sealing adhesive. Sealing of the substrates is done by putting a sealing adhesive, such as an epoxy adhesive, between the outer area of the display area on one of a pair of substrates and a corresponding area of the other substrate, and curing it by irradiation of ultraviolet rays or thermal processing. In this curing process by irradiation of ultraviolet rays, if the ultraviolet rays irradiate constituent members such as a semiconductor layer and an organic emitting layer formed in the pixel area, physical properties (or being called characteristics) of the constituent members of the semiconductor layer, the emitting layer, etc. may deteriorate. In the following, taking an image display apparatus using the organic EL panel as an example, effects by the irradiation of ultraviolet rays will be described.
The image display apparatus using the organic EL panel is produced by performing sequentially at least the following processes of: patterning an anode electrode formed on the light-transmitting first substrate, which is preferably a glass plate, for each pixel; forming banks for separating the later-described layered product formed on the anode electrodes for each element; forming a hole-injection layer for injecting electron holes from the anode electrode in each space separated by the banks; forming a hole-transport layer for transporting electron holes to the emitting layer; forming selectively the emitting layer composed of an organic layer for emitting one of red, green, and blue lights for each element of an emitting layered product; forming an electron-transport layer for transporting electrons from a cathode electrode; forming the cathode electrode for supplying electrons; and bonding the second substrate constituting a cap to the first substrate so as to be airtight with a sealant in order to block out the layered products from the outside.
Sealant is cured normally by irradiating ultraviolet rays from the substrate side on a sealing area on which the sealant is applied. Incidentally, there is a case where the substrate further undergoes thereafter a process of promoting the curing by thermal processing. In the image display apparatus using such an organic EL panel, in addition to deterioration of characteristics of the semiconductor layers, the emitting layer, etc. described above caused by irradiation of ultraviolet rays on the display area encircled by the sealing area, as disclosed in JP-A No. 176571/1999, peel is caused between the emitting layers and electrode layers, the constituent materials in the pixel area vary in characteristics due to effects of the outside air and moisture that have invaded the interior through the sealing part even if the airtight sealing has been done with the cap. Especially when the characteristics of the emitting layers deteriorated, non-emitting regions called dark spots or other defects occur in the display screen, and light emission of predetermined quality cannot be maintained as driving time accumulates.
Since the constituent materials are prone to be affected by the outside air and moisture as described above, it is a problem in the image display apparatus how the atmosphere at the time of sealing the two substrates may be controlled and how a state just after the sealing may be maintained. Moreover, since in the organic EL panel, its emitting layers are of organic materials, there is a possibility that gases might be generated after the sealing. Because of this, the substrates are sealed with an adsorbent capable of adsorbing the outside air and moisture that have invaded the interior of the panel passing through the sealant as well as generated gases. It is common that in order that this adsorbent does not interfere the emitting layered product composed of an emitting layer, the electrodes, etc., the second substrate constituting the cap is given the shape of a hollow that is fallen to its periphery or is provided with a rib formed on the periphery, and the adsorbent is disposed in the hollow area.
As a method for making the inner side of the second substrate constituting the cap hollow, there are a method for caving the inner side of a glass plate or a quartz plate by machining, sandblasting, or chemical etching and a method for integral molding the second substrate with a metal plate and a glass plate by means of a press etc. In the case where a metal plate is adopted for the cap, it is necessary to cure the sealant by irradiating ultraviolet rays from the side of the first substrate on which the emitting layer is formed. In the case where a glass plate is adopted for the cap, it is possible to cure the sealant by irradiating ultraviolet rays not only from the side of the substrate on which the emitting layer is formed but also from the side of the second substrate constituting the cap.
However, in the case where ultraviolet rays are irradiated from the side of the first substrate on which the emitting layer is formed, if an outlet part of electric terminals (external terminals) is made of a metal material, the ultraviolet rays are shielded by this external terminal, and hence it is impossible to cure the sealant sufficiently. Therefore, it is a certain method that the cap is made from the second substrate of a light-transmitting material such as a glass plate and the sealant is cured by irradiation of ultraviolet rays from this second substrate side. However, in either case, due to irradiation of ultraviolet rays in a curing process of the sealant, the ultraviolet rays are scattered in the first substrate on which the emitting layer is formed, or propagate through the first substrate as far as the display area to irradiate a display element (emitting layered product) made up of the emitting layer, and consequently an organic material thereof deteriorates and an emission life falls off. Thus, it is one of the problems that when the sealant is cured by ultraviolet rays, the emitting layered product made of the organic material is protected from the ultraviolet rays.
The image display apparatus using the organic EL panel is obtained by superposing the cap on the first substrate, which is preferably of a glass, on which the emitting layer is formed and sealing these members with a sealant, and thereby the emitting layered product comprising the organic material is shut off from the external atmosphere with the sealant. In the sealing process, the sealing is conducted in a space enclosed from the outside in order to enable the work to be done in an atmosphere where active gases and moisture are excluded as much as possible. However, as described above, after the sealing, the emitting layered product comprising the organic material may deteriorate in its emission properties (also called emission physical properties) because of moisture and gases of oxygen etc. that have invaded from the outside though the sealant to effect shortened emission life. Therefore, it is one of the problems that the first substrate on which the emitting layers are formed is aligned correctly to the second substrate constituting the cap and airtight sealing of these members is performed with the sealant surely. Such problems accompanying the irradiation of ultraviolet rays is not restricted to the image display apparatus using the organic EL panel, and similarly exist in various panel-type image display apparatuses, such as a liquid crystal display, a plasma electrical discharge display, and a field emission display.